The purpose of oil-well valves is to automatically stop effluent production in case of accident at the wellhead or downstream of it. The valves are hydraulically controlled to open from the surface and will automatically close due to a powerful return spring the moment there is a drop, controlled or accidental, of hydraulic pressure. Much research has been spent on these valves to improve them and they are widely used, in particular in offshore wells.
In one valve type, the sealing is achieved by a movable flap hinging on a cross shaft on the lower valve part so as to be capable either of closing perpendicularly to the valve axis due to spring means associated with said flap, or of closing due to the thrust of a tubular slide hydraulically displaced within the valve. Presently the flaps hinge about cylindrical shafts which are precisely set into a bore of the valve body. As a rule, an end screw locks the shaft, however such an assembly makes valve maintenance difficult. The removal of the flap shaft is difficult and usually done by hammering, whereby the shaft and the surrounding parts may be damaged. Furthermore, the holding screw is permanently immersed in the corrosive well fluid and therefore tends to break after some use, whereby disassembly is made substantially more difficult. Also, as regards manufacture, the precise machining of the flap shafts at very tight tolerances and their required precise assembly run up the costs.
The primary object of the present invention is to overcome the above cited drawbacks of the known flap-type valves in order to make maintenance easier and to reduce the manufacturing costs.
Another object of the invention is to eliminate the need for precise machining and setting of the flap shafts by providing in novel manner for their fixation both with regard to rotational and translational movement.
Further object of this invention is to permit exceedingly easy and quick assembly and disassembly of the flaps without any danger of degradation or jamming.
Still another object of the invention is to eliminate any auxiliary fixing component that might be subjected to the corrosive effects of the well fluids.
In order to facilitate comprehension, the valve of the invention is described being assumed in place in an oil well, the terms "high", "low", "upper", "lower" referring to that position.